Three-Dimensional Analysis of Turning Within Airborne Bird Flocks

Harold Pomeroy, University of Rhode Island


The three-dimensional structure of airborne pigeon flocks was monitored over time. Flocks changed both in overall shape, and in compactness during the execution of turns. Flight speeds of the flocks were sensitive to the vertical rather than the horizontal component of a turn. The compactness of flocks did not seem to change in relation to speed maintained during turns or sharpness of turns.

The cues to which birds responded in adjusting their flight paths may be important in determining flock compactness. Birds within flocks responded to each other's position and maintained positions close to each other. In a flock groups. of birds which maintained positions close to each other were observed as a distinct physical clump of nearest neighbors only if the overall flock structure was dispersed or was expanding over time. Birds flying on very different flight paths were occasionally observed to become temporary close neighbors due to the crossing of the arcs describing the flight paths of the birds. Under such conditions birds could possibly be detected as a physical clump of close neighbors within the overall structure of the flock.

Birds in flock performed aerial flight maneuvers while maintaining or increasing the compactness of the flock structure. The relative positions of birds within the flocks were not fixed. The repositioning of birds within the overall structure of turning and wheeling flocks indicates that adaptive strategies for predator avoidance could be based on a bird's ability to easily reposition within a flock, rather than on the distinctly different advantages of maintaining a peripheral or central location within the flock.

Behaviorally dominant and subordinate birds did not maintain specific positions within the airborne flocks. There was a tendency for birds of dissimilar dominance rank to be nearest neighbors within the airborne flocks.